Populate items in drop down lists from internal/external source
Drop down lists is issues, such as used in custom fields, versions, assigned_to, among others, are part of the html code Redmine sends to the user. If the number of items is too big (thousands of lines), it generates a very inneficient large select in the middle of the html code that redmine sends the user.
This large html is not cacheable by the browser, and it is sent regardless of it being used. It slows down browsing using next/previous issue significantly, as well as when changing issue type, which reloads all fields.